Zoo animals experience longer life spans than wild counterparts

Most mammals have a greater life expectancy in zoos, rather than in the wild, concludes a recent study. Published in Scientific Reports by researchers from the University of Lyon in France and the University of Zurich in Switzerland, the study compared four survival metrics in order to reach this conclusion.

The international research team compared the baseline longevity, mortality, onset of senescence and rate of senescence between 59 different mammal species. Senescence refers to the deterioration of an animal or its cells during the aging process.

After studying both sexes of the species within zoos and within the wild, the researchers determined that 84 percent of species living in zoos experienced a longer lifespan in contrast to their counterparts living in the wild. The benefit of living in a zoo is most pronounced in species who typically have a high mortality rate in the wild, a high reproductive rate and a short life span.

Captive female lions, for example, possess a higher level of longevity and lower rate of mortality when compared to their wild counterparts. Female lions in zoos live more than 25 years on average, while wild female lions live an average of 15 years.

In contrast, species with a low mortality rate in the wild, a low reproductive rate and a relatively long life span benefit less from living in zoos. In comparison to female mammals, male mammals tend to benefit slightly more from living in captivity, although many of the patterns observed from the analysis of survival metrics are similar across both sexes.

In 76 percent of the male species analyzed, the age of the captive animal at the onset of senescence was either identical or higher than that same animal living in the wild. The rate of senescence in this same demographic was also lower in comparison to wild male mammals.

According to the study, mammalian species enjoy longer life spans in captivity due to the constant accessibility of food, shelter and water. Additionally, zoo animals are typically separated by species and thus do not encounter predators. Violent encounters between zoo animals are kept to a minimum and medical care is constantly provided by veterinarians and zoo staffers.

In regard to mammals with slower lifecycles, spending a lifetime in captivity can actually be detrimental rather than beneficial. These mammals may actually have a slightly lower level of longevity and higher senescence rate when compared to their wild counterparts.

“With regard to long-lived species that generally have lower mortality rates in the wild, there is less that zoos can protect them from,” said Marcus Clauss, a professor of nutrition and biology of zoo and wild animals at the University of Zurich. “As such, the effect is not as great and, indeed, in some cases is even reversed,” he continued.

According to prior studies that analyzed the breeding of captive chimpanzees and Asian elephants, mammals in captivity often breed earlier than mammals in the wild, which may be responsible for this detriment.

Further analysis on the mammals’ life expectancy in zoos determined that carnivores experience enhanced life expectancy in zoos, but are still not free of issues. Polar bears, for example, are prone to breeding difficulties, poor health and repetitive stereotypic behavior when kept in captivity rather than the wild.

“All 15 carnivore species in our dataset attained greater longevity at the zoo… It seems that even for predators, life in the wild is not necessarily without its perils,” Clauss concluded.

While prior studies of this nature would often analyze less than 25 different species, this most recent study is unique in the sheer size of its species sampling. Past studies were also restricted to a small taxonomic range that did not account for interspecies diversity. Flaws were often found in analyses that included no other survival metric beside senescence rate. As a result of these flaws, these studies often yielded conflicting results.

Despite issues with keeping animals in captivity, such as the aforementioned detriments faced by mammalian species with a slower pace of life, zoos can still be considered useful in nearly all cases. Prior studies have proven that mammals with slower paces of life are more prone to extinction, thus the studies stress that it is important to keep at least a small population of these sorts of mammals in captivity to better preserve the species as a whole.